Direct-heated flow measuring apparatus having improved response characteristics

ABSTRACT

In a direct-heated flow measuring apparatus including a substrate having a film resistance pattern and a supporting member for supporting the substrate, the supporting member has good heat dissipation characteristics. Provided between the substrate and the supporting member is a heat transfer throttling portion.

This is a continuation of application Ser. No. 828,452, filed Feb. 11,1986, which was abandoned upon the filing hereof.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The present invention relates to a direct-heated flow measuringapparatus having a film resistor which serves as a temperature detectingmeans as well as an electric heater. Such a direct-heated flow measuringapparatus can be used, for example, for measuring the flow rate ofengine intake air.

(2) Description of the Related Art

Generally, in an internal combustion engine, the amount of intake air isone of the most important parameters for controlling the fuel injectionamount, ignition timing, and the like. A gas-flow measuring apparatus,i.e., an airflow meter, is provided for measuring the same. One of themore common prior art airflow meters is the vane-type, which is,however, disadvantageous in scale, response speed characteristics, andthe like. Recently, airflow meters having temperature-dependentresistors have been developed, which are advantageous in scale, responsespeed characteristics, and the like.

There are two types of airflow meters having temperature-dependentresistors, i.e., the heater-type and direct-heated type. The heater-typeairflow meter may consist of an electric heater resistor provided in anintake-air passage of an engine and two temperature-dependent resistorsarranged on the upstream and downstream sides of the electric heaterresistor. In this case, the temperature-dependent resistor on thedownstream side is used for detecting the temperature of air heated bythe heater resistor, while the temperature-dependent resistor(temperature-compensating resistor) on the upstream side is used fordetecting the temperature of non-heated air. The current flowing throughthe heater resistor is controlled for a constant difference intemperature between the two temperature-dependent resistors, therebydetecting the voltage applied to the heater resistor as the mass flowrate of air.

In this heater-type airflow meter, if no temperature-compensatingresistor upstream is provided and the current of the heater resistor iscontrolled for a constant temperature of the downstreamtemperature-dependent resistor, the voltage applied to the heaterresistor is detected as the volume flow rate of air.

On the other hand, the direct-heated type airflow meter may consist of afilm resistor which serves not only as an electric heater, but also as atemperature-detecting means for detecting the temperature of the heatedair. Also, the direct-heated type airflow meter may consist of atemperature-dependent resistor (temperature-compensating resistor) fordetecting the temperature of non-heated air. Thus, the current flowingthrough the film resistor is controlled for a constant difference intemperature between the film resistor and the temperature-compensatingresistor, thereby detecting the voltage applied to the film resistor asthe mass flow rate of air. In this direct-heated type airflow meter,too, if no temperature-compensating resistor is provided and the currentof the heater resistor is controlled for a constant temperature of thefilm resistor, the voltage applied to the film resistor is detected asthe volume flow rate of air.

Since the film resistor of the direct-heated type airflow meter servesas a temperature-detecting means for heated air, that is, no additionaltemperature detecting means for heated air is necessary, thedirect-heated type airflow meter is smaller in size than the heater-typeairflow meter.

In the direct-heated type airflow meter, the film resistor may consistof an insulating substrate such as a ceramic substrate ormonocrystalline silicon substrate, a film resistance pattern of platinum(Pt), gold (Au), etc. on the insulating substrate, and a heat-resistantresin on the resistance pattern.

Usually, the response characteristics and dynamic range of thedirect-heated type airflow meter are dependent upon the heat mass andadiabatic efficiency of the film resistance pattern, which serves notonly as a heating means but also as a temperature detecting means. Inorder to obtain the most excellent response characteristics and largestdynamic range, the film resistance pattern should be ideally in acompletely floating state in the air stream. In the prior art, however,the film resistor including the film resistance pattern has had anapproximately definite width over the lengthwise direction thereof.Accordingly, the adiabatic efficiency is relatively low, thus reducingthe response characteristics and dynamic range of the heat-directedairflow meter.

To alleviate this problem, a direct-heated type airflow meter may besuggested in which an aperture is provided between the heating andtemperature detecting portion of the substrate including the filmresistor and its supporting member of the substrate, thereby creating athrottling effect on the heat transfer, and thus increasing theadiabatic efficiency of the heating and temperature detecting portionand improving the response speed and dynamic range of the airflow meter.

Note that, usually, the heat transfer throttling portion has a smallcross-section in order to obtain a further adiabatic efficiency.

However, even if such a heat transfer throttling portion is provided,some heat is still transmitted to the supporting member and as a result,it takes a long time for the heat transmitted to the supporting member,such as a ceramic having bad dissipation characteristics, to becomestable, which means that the airflow meter has a bad responsecharacteristic. Also, since the connections from the substrate to a staywithin a duct are usually conventionally carried out by lead terminals(pins), the heat of the heating and temperature-detecting portion of thesubstrate is transmitted via the lead terminals to the duct. In otherwords, the adiabatic effect of the substrate is small, and accordingly,the heat loss is large, thereby also deteriorating the responsecharacteristics of the airflow meter.

Further, in the conventional direct-heated airflow sensor for detectingthe mass flow rate of air, the film resistance pattern as the heater andtemperature-detecting portion and the temperature-compensating resistorare disposed at quite different positions. For example, the filmresistance pattern is provided within the duct, and thetemperature-compensating resistor is provided outside of the duct.Therefore, due to the difference in heat capacity between the filmresistance pattern including its supporting system and thetemperature-compensating resistor including its supporting system, thetransient temperature characteristics of the system of the filmresistance pattern are different from those of the system of thetemperature-compensating resistor. As a result, the difference intemperature between the film resistance pattern and thetemperature-compensating resistor during a transient state isfluctuated, thereby generating an error in the measured flow rate ofair.

SUMMARY OF THE INVENTION

It is a principal object of the present invention to provide adirect-heated flow measuring apparatus having improved responsecharacteristics.

It is another object of the present invention to provide a direct-heatedflow measuring apparatus having a small error of a measured flow rate.

According to the present invention, in a direct-heated flow measuringapparatus including a substrate having a film resistance pattern and asupporting member for supporting the substrate, the supporting memberhas good heat dissipation characteristics. Provided between thesubstrate and the supporting member is a heat transfer throttlingportion. Also, an adiabatic member is inserted between the filmresistance pattern and the supporting member, and wire bonding isimposed as the electrical connections between the film resistancepattern and the supporting member. As a result, since heat transmittedto the supporting member is positively dissipated to the fluid such asan airstream via a supporting member such as aluminium or copper havinggood heat dissipation characteristics, the heat transmitted to thesupporting member becomes stable promptly, thereby improving theresponse characteristics of the flow rate sensors. Also, since thesubstrate is supported by the adiabatic member, and the bonding wiresare thin as compared with the lead terminals (pins), the heat loss ofthe substrate becomes small, thereby improving the accuracy of detectionof the flow rate, and thus further improving the responsecharacteristics.

Further, if a temperature-compensating resistor is provided in theheat-directed flow measuring apparatus, the film resistance pattern andthe temperature-compensating resistor have the same configuration, thesame substrate, and the same supporting member. As a result, thetransient temperature characteristics of the system of the filmresistance pattern are the same as those of the system of thetemperature-compensating resistor. Therefore, the fluctuation of thedifference in temperature between the film resistance pattern and thetemperature-compensating resistor during a transient state is small, andaccordingly, an error in the measured flow rate is small.

Other objects, features and characteristics of the present invention, aswell as the methods and operation and functions of the related elementsof the structure, and the combination of parts and economies ofmanufacture, will become apparent upon consideration of the followingdescription and the appended claims with reference to the accompanyingdrawings, all of which form a part of the specification, wherein likereference numerials designate corresponding parts in the variousfigures.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be more clearly understood from thedescription as set forth below with reference to the accompanyingdrawings, wherein:

FIG. 1 is a schematic diagram showing the overall configuration of aninternal combustion engine including a direct-heated type flow measuringapparatus according to the present invention;

FIG. 2 is a circuit diagram of the sensing circuit of FIG. 1;

FIGS. 3, 4, and 5 are partially cutaway, perspective views illustratingfirst, second, and third embodiments of the, direct-heated flowmeasuring apparatus according to the present invention;

FIG. 6 is an exploded, perspective view of the film resistor and, itssupporting member of FIG. 3;

FIG. 7 is a cross-sectional view of the bonding portion of the filmresistor and its supporting member of FIG. 3;

FIG. 8 is a diagram showing the characteristics of the adiabatic, memberof FIGS. 3, 4, and 5;

FIG. 9A is a plan view of an example of the film resistor of FIGS. 3, 4,and 5;

FIGS. 9B and 9C are cross-sectional views taken along the lines B-C andC-C, respectively, of FIG. 9A;

FIG. 10A is a plan view of another example of the film resistor of FIGS.3, 4, and 5;

FIGS. 10B and 10C are cross-sectional views taken along the lines B-Cand C-C, respectively, of FIG. 10A;

FIG. 11A is a plan view of a further example of the film resistor ofFIGS. 3, 4, and 5;

FIGS. 11B and 11C are cross-sectional views taken along the lines B-Cand C-C, respectively, of FIG. 11A;

FIG. 12 is a plan view illustrating a fourth embodiment of thedirect-heated flow measuring apparatus according to the presentinvention;

FIGS. 12B and 12C are cross-sectional views taken along the lines B-Cand C-C, respectively, of FIG. 12A;

FIGS. 13A and 13B are perspective views of modifications of the, bondingportion of the film resistor and its supporting member of FIG. 6;

FIG. 13C is a cross-sectional view taken along the line C-C of FIG. 13B;

FIGS. 13D and 13E are modifications of FIG. 3C;

FIG. 14 is a side view illustrating a fifth embodiment of thedirect-heated flow measuring apparatus according to the presentinvention;

FIG. 15 is a cross-sectional view illustrating a sixth embodiment of thedirect-heated flow measuring apparatus according to the presentinvention; and

FIGS. 16A, 16B, 17A, and 17B are timing diagrams for explaining theeffect of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In FIG. 1, which illustrates the overall configuration of an internalcombustion engine including an air flow measuring apparatus according tothe present invention, reference numeral 1 designates a spark ignitionengine for driving an automobile in which air for combustion is suckedthrough an air cleaner 2, a rectifier grid 3 for making the air flowuniform, and an intake air passage 4. Provided in the intake air passage4 is a throttle valve 5 arbitrarily operated by a driver. The flowmeasuring apparatus is provided in the intake air passage 4 between therectifier grid 3 and the throttle valve 5.

The flow measuring apparatus includes a sensing portion inside of theintake air passage 4 and a sensing circuit 10 outside of the intake airpassage 4. The sensing portion includes a measuring tube (or duct) 6fixed by a stay 7 to the intake air passage 4. A film resistor (filmresistance pattern) 8 and a temperature-compensating resistor 9 fordetecting the temperature of non-heated air are both provided inside ofthe duct 6. However, the temperature-compensating resistor 9 issubstantially unaffected by the heat generated from the film resistor 8.The film resistor 8 and the temperature-compensating resistor 9 areconnected to the sensing circuit 10 mounted on a hybrid board.

The sensing circuit 10 controls the current flowing to the film resistor8 to generate heat for a constant difference in temperature between thefilm resistor 8 and the temperature-compensating resistor 9. Also, thesensing circuit 10 generates an output voltage V_(Q) and transmits it toa control circuit 11, which includes, for example, a microcomputer. Thecontrol circuit 11 also receives various kinds of detecting signals suchas an engine speed signal Ne (not shown) and an engine coolanttemperature signal THW (not shown) and controls the valve opening timeperiod of a fuel injection valve 12 and the like.

The sensing circuit 10 of FIG. 1 will be explained with reference toFIG. 2. In FIG. 2, the sensing circuit 10 includes resistors 101 and 102which form a bridge circuit with the film resistor 8 and thetemperature-compensating resistor 9; a comparator 103; a transistor 104controlled by the comparator 103; and a voltage buffer 105. The sensingcircuit 10 operates as follows. When the amount of air flowing throughthe intake air passage 4 increases, thus reducing the temperature of thefilm resistor 8, which is, in this case, a resistance element such as aplatinum resistance having a positive temperature coefficient, theresistance value thereof decreases so as to satisfy the followingcondition:

    V.sub.1 <V.sub.R

where V₁ is the potential at the node between the resistor 101 and thefilm resistor 8 and V_(R) is the potential at the node between theresistor 102 and the temperature-compensating resistor 9. As a result,the output potential of the comparator 103 is reduced, therebyincreasing the conductivity of the transistor 104. Therefore, the heatgenerated by the film resistor 8 is increased and, simultaneously, thecollector potential of the transistor 104 is increased, so that theoutput voltage V_(Q) of the voltage buffer 105 is also increased.

Contrary to this, when the amount of air flowing through the intake airpassage 4 decreases, thus increasing the temperature of the filmresistor 8, the resistance value thereof increases so as to satisfy thefollowing condition:

    V.sub.1 >V.sub.R.

As a result, the output potential of the comparator 103 is increased,thereby decreasing the conductivity of the transistor 104. Therefore,the heat generated by the film resistor 8 is decreased and,simultaneously, the collector potential of the transistor 104 isdecreased, so that the output voltage V_(Q) of the voltage buffer 105 isalso decreased.

Thus, feedback control is performed upon the temperature of the filmresistor 8 for a constant difference in temperature between the filmresistor 8 and the temperature-compensating resistor 9, which, in thiscase, detects the temperature of ambient air. Thus, the output voltageV_(Q) of the output buffer 105 indicates the amount of air flowingthrough the intake air passage 4.

In FIG. 3, which illustrates a first embodiment of the presentinvention, the film resistor 8 and the temperature-compensating resistor9 are fixed to supporting members 21 and 22, respectively, arranged inparallel with respect to the airstream. The film resistor 8 is fixed viaadiabatic members 23a and 23b to the supporting member 21, and, in thiscase, the adiabatic members serve as heat transfer throttling portionsfor the film resistor 8, which serves as an electric heater as well as atemperature-detecting means. The adiabatic members 23a and 23b for theheat transfer throttling portions are made of material having a smallspecific heat and a small heat conductivity, such as ceramic, polyimidresin, quartz, or glass, and accordingly, they also serve aselectrically insulating members. Therefore, the film resistor 8 andelectrodes 21a and 21b formed on the supporting member 21 areelectrically connected by electric conductive wires 24a and 24b by wirebonding. Note that the electrodes such as 21a are adhered to thesupporting members such as 21 by heat-resistant adhesives.

Further, according to the present invention, the supporting member 21 ismade of a metal such as aluminium or copper having a large thermalconductivity and a small specific heat. Therefore, the heat transmittedfrom the film resistor 8 via the adiabatic members 23a and 23b as theheat transfer throttling portions to the supporting member 21 ispromptly dissipated to the airstream. That is, most of the heatgenerated by the film resistor 8 is dissipated from the film resistor 8itself due to the presence of the adiabatic members 23a and 23b, and onepart of the heat is transmitted via the adiabatic members 23a and 23b tothe supporting member 21. However, this part is also dissipated into theairstream. Therefore, heat transmitted via the duct 6 and the stay 7 toportions other than the airstream is remarkably reduced.

Note that, in order to make the transient temperature characteristics ofthe system of the film resistor 8 conform with those of the system ofthe temperature-compensating resistor 9, the film resistor 8 and thetemperature-compensating resistor 9 are of the same substrate material,the same heat capacity, and the same dimension, and are fixed by thesame method with adiabatic material (not shown) to the supportingmembers 21 and 22 which are the same as each other.

Note that, if the transient temperature characteristics of the system ofthe film resistor 8 are different from those of the system of thetemperature-compensating resistor 9, the balance of the bridge circuitof FIG. 2 is destroyed, thereby generating an error in the detection ofa measured flow rate.

Further, in FIG. 3 since the film resistor 8 and thetemperature-compensating resistor 9 are provided on separate substratesand are apart from each other, the heat amount generated by the filmresistor 8 has little affect on the temperature-compensating resistor 9.

In FIG. 4, which illustrates a second embodiment of the presentinvention, apertures 25 for dissipating heat are added to the elementsof FIG. 2. Thus, the heat dissipation characteristics of the supportingmember 21 are further improved, and as a result, the heat transmittedfrom the film resistor 8 via the adiabatic members 23a and 23b as theheat transfer throttling portions to the supporting member 21 ispromptly dissipated into the airstream. Therefore, heat transmitted viathe duct 6 and the stay 7 to portions other than the airstream isfurther remarkably reduced.

Note that, in order to make the transient temperature characteristics ofthe system of the film resistor 8 conform with those of the system ofthe temperature-dependent resistor 9, the same number of heatdissipation apertures 25 are also provided at the same positions in thesupporting member 22 by which the temperature-compensating temperature 9is supported.

In FIG. 5, which illustrates a third embodiment of the presentinvention, heat dissipating fins 26 are added to the elements of FIG. 2.Thus, the heat dissipation characteristics of the supporting member 21are also further improved, and as a result, the heat transmitted fromthe film resistor 8 via the adiabatic members 23a and 23b as the heattransfer throttling portions to the supporting member 21 is promptlydissipated into the airstream. Therefore, heat transmitted via the duct6 and the stay 7 to portions other than the airstream is furtherremarkably reduced.

Note that, in order to make the transient temperature characteristics ofthe system of the film resistor 8 conform with those of the system ofthe temperature-compensating resistor 9, the same number of heatdissipating fins (not shown) are also provided at symmetrical positionsin the supporting member 22 by which the temperature-compensatingresistor 9 is supported.

Further, the second embodiment as shown in FIG. 4 and the thirdembodiment as shown in FIG. 5 in combination can be applied to a flowmeasuring apparatus. That is, in order to improve the heat dissipationcharacteristics of the supporting members, it is possible to provideboth the heat dissipating apertures and the heat dissipating fins in thesupporting members.

Note that, as illustrated in FIGS. 3-5, a part of the substrate of thefilm resistor 8 which is adhered to the adiabatic member 23A or 23B, anda part of the supporting member 21 adhered to the adiabatic member 23Aor 23B, have the same cross-sectional outline as the adiabatic member23A or 23B. This cross-sectional outline is a smaller area than that ofthe superposed surfaces between the film resistor substrate 8 and thesupporting member 21.

FIG. 6 is an exploded perspective view of the film resistor 8 and thesupporting member 21 of FIG. 3, and FIG. 7 is a partial cross-sectionalview for explaining the bonding method of the film resistor 8 and thesupporting member 21 of FIG. 3. As illustrated in FIG. 6, positioningholes 23a' and 23b' for the adiabatic members 23a and 23b are formed inadvance in the supporting member 21 made of aluminium or copper, and asshown in FIG. 7, adhesives 27 are coated on both surfaces of theadiabatic member 23a (23b), so that the film resistor 8 is fixed to thesupporting member 21. Also, in FIG. 6, provided on the under surface ofthe electrodes 21a and 21b are insulating layers 21a' and 21b' of suchas polyimid resin, so that the electrodes are electrically insulatedfrom the supporting member 21, and as shown in FIG. 7, the electrodes21a (21b) are fixed by adhesives 27' to the supporting member 21. As isapparent from FIGS. 6 and 7, each of the adiabatic members 23a and 23bhas a smaller capacity than the substrate 8 and the supporting member21.

Note that the adhesives 27 and 27' are heat-resistant resin.

FIG. 6 shows the cross-sectional of the adiabatic member 23A/23B havinga smaller section than of the superposed surfaces between the filmresistor substrate 8 and the supporting member 21.

FIG. 8 is a diagram showing the response characteristics of theadiabatic members of FIGS. 3 to 5. For the adiabatic members 23a and23b, their adiabatic effect should be increased and their heat massshould be decreased. In view of this, as explained above, the adiabaticmembers are made by using material such as polyimid resin, and the likehaving a small thermal conductivity and a small specific heat. Also, thethickness of the adiabatic members is an important parameter. That is,as shown in FIG. 8, as the thickness of the adiabatic members 23a and23b increases, the heat mass increases, thereby deteriorating theresponse characteristics although the adiabatic effect is increased.Contrary to this, as the thickness of the adiabatic members 23a and 23bdecreases, the adiabatic effect decreases thereby deteriorating theresponse characteristics, although the heat mass is decreased. Asillustrated in FIG. 8, where the adiabatic members 23a and 23b usepolyimid resin, their thickness is preferably 50 to 60 μm.

The film resistor of FIGS. 3 to 5 will be explained with reference toFIGS. 9A to 9C. Note that FIGS. 9B and 9C are cross-sectional viewstaken along the lines B-B and C-C, respectively, of FIG. 9A. As shown inFIG. 9A, an insulating layer such as silicon dioxide (SiO₂), which isnot shown, is evaporated and is etched on a monocrystalline siliconsubstrate 81 having a thickness of 200 to 400 μm, thereby obtaining afilm resistance pattern 82 which has a portion 82a indicated by a dottedframe serving as a heating and temperature-detecting portion. Note thatthe thickness of the silicon substrate 81 on the heating andtemperature-detecting portion 82a is very thin as shown in FIGS. 9B and9C, thereby decreasing the heat mass thereof.

In the embodiments of FIGS. 3 to 5, although the throttling of the heattransfer is carried out by the adiabatic member 23a and 23b, it can becarried out by reducing the width of the heat passage of the substrateof the film resistor 8. Examples of this are illustrated in FIGS. 10A to10C, and FIGS. 11A to 11C. Note that, in this case, since the adiabaticmembers can be deleted, the electrical connections between the filmresistor 8 and the electrodes 21a and 21b can be carried out directlyand not by bonding wires.

FIG. 10A shows another example of the film resistor 8, and FIGS. 10B and10C are cross-sectional views taken along the lines B-B and C-C,respectively, of FIG. 10A. As shown in FIG. 10A, an insulating layersuch as SiO₂, which is not shown, is evaporated and is etched on amonocrystalline silicon substrate 81', thereby obtaining a filmresistance pattern 82' which has a portion 82'a indicated by a dottedframe serving as a heating and temperature-detecting portion.

Formed on the sides of the heating and temperature-detecting portion82'a are apertures 83'a and 83'b, thereby imposing the throttling of theheat transfer upon the heating and temperature-detecting portion 82'a,thus increasing the adiabatic effect thereof. Further, the thickness ofthe silicon substrate 81' on the heating and temperature-detectingportion 82'a is very thin as shown in FIGS. 10B and 10C, therebydecreasing the heat mass thereof. Note that reference 81'a designates atrap for trapping suspended particles or the like.

FIG. 11A shows still another example of the film resistor 8, and FIGS.11B and 11C are cross-sectional views taken along the lines B-B and C-C,respectively, of FIG. 11A. Also in FIGS. 11A to 11C, on amonocrystalline silicon substrate 81", a film resistor 82" is formed byevaporating and etching an insulating layer such as SiO₂, which is notshown, and the portion 82"a indicated by a dotted frame serving as aheating and temperature-detecting portion.

The substrate portions 81"a and 81"b on the sides of the heating andtemperature-detecting portion 82"a is narrow when compared with theportion 82"a so that a throttle for the heat transfer is formed, therebyincreasing the adiabatic effect of the heating and temperature-detectingportion 82"a. In the same way as in FIGS. 10A to 10C, the thickness ofthe silicon substrate 81" on the heating and temperature-detectingportion 82"a is very thin as shown in FIGS. 11B and 11C, therebydecreasing the heat mass thereof.

In FIGS. 12A, 12B, and 12C, which illustrate a fourth embodiment of thepresent invention, the film resistor 8 is fixed to a supporting member21' having good heat dissipation characteristics, which has apertures21'c and 21'd for the throttling of the heat transfer. Also, in thiscase, the throttling of the heat transfer is carried out by adiabaticmembers or by reducing the width of the heat passage of the substrate.Therefore, in the same way as in the above-mentioned embodiments, mostof the heat generated from the film resistor 8 is dissipated from thefilm resistor 8 itself into the airstream, and one part of it istransmitted via the throttling portion of heat transfer to thesupporting member 21'. However, this part is also dissipated into theairstream. In this case, since the throttling of the heat transfer isalso imposed on the supporting member 21', the heat generated by thefilm resistor 8 transmitted via the duct 6 and the stay 7 to portionsother than the airstream is further reduced. Note that reference numeral28 designates a protector against backfiring.

FIG. 13A is a modification of the film resistor 8 and its supportingmember of FIG. 6. That is, the electrode 21a is provided in a recessformed within the supporting member 21. In this case, if the size of theadiabatic member 23a is reduced while sufficiently maintaining theretentive force of the film resistor 8, the heat mass of the adiabaticmember 23a is reduced.

In FIG. 13B, which is also a modification of FIG. 6, and FIG. 13C, whichis a cross-sectional view taken along the line C-C of FIG. 13B, in orderto protect the electric conductive wire 24a against backfiring or thelike, and to prevent it from being stained, a cover 31 and a mold resin32 are added to the elements of FIG. 13A.

The assembling of the portion as shown in FIGS. 13B and 13C is carriedout as follows. The film resistor 8 is fixed by the adiabatic member 23acoated by adhesives to the supporting member 21, and the wire 24a ismade by wire bonding. Then, after imposing the mold resin 32 onto thesupporting member 21, the protection cover 31 is attached thereto, thuscompleting the assembly of the portion as shown in FIGS. 13B and 13C.

In FIG. 13D, which is a modification of FIG. 13C, the supporting member21 and the cover 31 has curls (curled edges) 21e and 31a at their ends,thereby effectively carrying out the protection of the electricconductive wire 24a against backfiring and preventing the wire 24a frombeing stained by depositions.

In FIG. 13E, which is a modification of FIG. 13D, the film resistor 8 isfixed by two adiabatic members 33a and 33b to the cover 31 as well asthe supporting member 21, thereby further effectively carrying out theprotection of the electric conductive wire 24a against backfiring andpreventing the wire 24a from being stained by depositions.

In FIG. 14, which illustrates a fifth embodiment of the presentinvention, the film resistor 8 is in proximity to thetemperature-compensating resistor 9, and the temperature-compensatingresistor 9 is provided upstream of the film resistor 8. That is, thefilm resistor 8 and the temperature-compensating resistor 9 are adheredonto the same supporting member 21", so that the system of the filmresistor 8 and the system of the temperature-compensating resistor 9have the same heat capacity, and accordingly, the transient temperaturecharacteristics of the system of the film resistor 8 are the same asthose of the system of the temperature-compensating resistor 9. As aresult, the fluctuation of the difference in temperature between thefilm resistor 8 and the temperature-compensating resistor 9 during atransient state is also small, and accordingly, an error in the measuredflow rate is small.

Note that in FIG. 14, since the temperature-compensating resistor 9 isprovided upstream of the film resistor 8, the heat generated by the filmresistor 8 has little affect on the temperature-compensating resistor 9.

In FIG. 15, which illustrates a sixth embodiment of the presentinvention, only one supporting member 21" is provided, and the filmresistor 8 and the temperature-compensating resistor 9 are adhered tothe front and back, respectively, thereof. As a result, the system ofthe film resistor 8 and the system of the temperature-compensatingresistor 9 have the same heat capacity, and accordingly, the transienttemperature characteristics of the system of the film resistor 8 are thesame as those of the system of the temperature-compensating resistor 9.As a result, the fluctuation of the difference in temperature betweenthe film resistor 8 and the temperature-compensating resistor 9 during atransient state is also small, and accordingly, an error in the measuredflow rate is small.

Note that in FIG. 15, since the film resistor 8 and thetemperature-compensating resistor 9 are provided on opposite sides toeach other, the heat generated by the film resistor 8 has little affecton the temperature-compensating resistor 9.

As shown in FIGS. 16A and 16B, in the prior art, when the film resistor8 and the temperature-compensating resistor 9 are positioned at quitedifferent places, the change of the temperature T₁ of the film resistor8 is different from the change of the temperature of thetemperature-compensating resistor 9, where the ambient temperature Ta ischanged. Note that FIG. 16A shows the case wherein no current issupplied to the film resistor 8. That is, at the rise of the ambienttemperature Ta, the temperature T₁ of the film resistor 8 rises quicklyas compared with the temperature T₂ of the temperature-compensatingresistor 9, so that the heat generated by the film resistor 8 isreduced. Therefore, in order to obtain a definite difference intemperature, the output V_(Q) is reduced by ΔV₁ as indicated by FIG.16B. On the other hand, at the fall of the ambient temperature Ta, thetemperature T₁ of the film resistor 8 falls quickly as compared with thetemperature T₂ of the temperature-compensating resistor 9, so that theheat generated by the film resistor 8 is increased. Therefore, in orderto obtain a definite difference in temperature, the output V_(Q) isincreased by ΔV₂ as indicated by FIG. 16B. Contrary to this, accordingto the present invention, the change of each of the film resistor 8 andthe temperature-compensating resistor 9 is the same as shown in FIG.17A, and accordingly, no error of the output V_(Q) is generated, asshown in FIG. 17B.

In the above-mentioned embodiments, although the substrate of the filmresistor 8 uses monocrystalline silicon, ceramic or glass also can beused. Also, although a resistance pattern as the heating andtemperature-detecting portion is formed on a monocrystalline siliconsubstrate, a diffusion resistor can be formed within the monocrystallinesilicon substrate. Also, corrosion-proof metal can be used as theabove-mentioned electrodes (sheets) 21a (21b) and the electricconductive wire 24a (24b). For example, the electrodes use Au, Pt, orthe like, and the electric conductive wire uses Au. Further, althoughboth of the ends of the film resistor (or the temperature-compensatingresistor) are supported by the same supporting member, only one endthereof can be supported thereby, and each end can be supported byseparate supporting members. The present invention can be applied toflow rate sensors other than airflow sensors, such as liquid flow ratesensors.

The present invention can be also applied to a digital (pulse) type flowrate sensor controlled by a trigger pulse. That is, in this sensor whensuch a trigger pulse is given to initiate heating of a heater resistor.Then, the heating of the heater resistor continues until a constantdifference in temperature between two temperature-dependent resistors isgenerated, or until the downstream temperature-dependent resistorreaches a constant value. In this case, the heating time period isdetected as the mass flow rate of air or the volume flow rate of air.Such a trigger pulse control has an advantage in that the powerdissipation is good. Note that such trigger pulse control is possible ina direct-heated rate sensor.

As explained above, according to the present invention, the heattransmitted to the supporting member can be positively dissipated viathe supporting member having a good heat dissipation characteristics tothe fluid such as air, and as a result, the heat transmitted to thesupporting member becomes promptly stable, thereby improving theresponse characteristics of the flow measuring apparatus. Also, the heatloss of the substrate, on which the film resistor is formed, is reduced,thereby improving the accuracy of flow rate detection. Further, thefluctuation of the difference in temperature between the film resistorand the temperature-compensating resistor during a transient state canbe small, and accordingly, an error in the measured flow rate can besmall.

While the invention has been described in connection with what ispresently considered to be the most practical and preferred embodiment,it is to be understood that the invention is not limited to thedisclosed embodiment, but, on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

We claim:
 1. A direct-heated flow measuring apparatus for measuring theflow rate within a passage comprising;a planar substrate that is formedof monocrystalline silicon; a film resistance pattern formed partiallyat said substrate; a supporting plate, fixed to said passage, forsupporting said substrate, said supporting plate having good heatdissipation characteristics; at least one adiabatic member disposedbetween said substrate and said supporting plate; and electric powercontrol means, connected to said film resistance pattern, forcontrolling the heat generated by said film resistance pattern, one partof a surface of said planar substrate and one part of a surface of saidsupporting plate being superimposed on each other via said adiabaticmember, the cross-section of said adiabatic member being smaller thanthe superimposed area of said planar substrate and said supportingplate.
 2. An apparatus as set forth in claim 1, wherein apertures areprovided in said supporting member.
 3. An apparatus as set forth inclaim 1, wherein fins for dissipating heat are provided in saidsupporting plate.
 4. An apparatus as set forth in claim 1, wherein saidsupporting plate is made of a material having a relatively largerthermal conductivity than a thermal conductivity of said adiabaticmember.
 5. An apparatus as set forth in claim 4, wherein said materialis metal.
 6. An apparatus as set forth in claim 5, wherein said metal isone of aluminium and copper.
 7. An apparatus as set forth in claim 1,wherein said adiabatic member is inserted between an edge of saidsupporting plate and said substrate.
 8. An apparatus as set forth inclaim 1, wherein said resistance pattern is formed on saidmonocrystalline silicon.
 9. An apparatus as set forth in claim 1,wherein a diffusion resistance is formed as said film resistance patternin said monocrystalline silicon.
 10. An apparatus as set forth in claim1, further comprising a temperature-compensating resistor for detectingthe temperature of non-heated fluid in the fluid stream, saidtemperature-compensating resistor being substantially unaffected by theheat generated from said film resistance pattern, said electric powercontrol means controlling the heat generated by said film resistancepattern and said temperature-compensating resistor.
 11. An apparatus asset forth in claim 10, wherein a system of said temperature-compensatingresistor has the same configuration as a system of said film resistancepattern, the system of said temperature-compensating resistor beingsymmetrical to the system of said film resistance pattern with respectto the fluid stream.
 12. An apparatus as set forth in claim 11, whereinthe system of said temperature-compensating resistor comprises asupporting means different to the system of said film resistancepattern.
 13. An apparatus as set forth in claim 11, wherein the systemof said temperature-compensating resistor comprises the same supportingmeans as the system of said film resistance pattern.
 14. An apparatus asset forth in claim 10, wherein a system of said temperature-compensatingresistor has the same configuration as a system of said film resistancepattern, the system of said temperature-compensating resistor beingdisposed upstream of the system of said film resistance pattern.
 15. Anapparatus as set forth in claim 14, wherein the system of saidtemperature-compensating resistor comprises the same supporting means asthe system of said film resistance pattern.
 16. An apparatus as setforth in claim 1, wherein said adiabatic member is made of an insulatingmaterial.
 17. An apparatus as set forth in claim 16, furthercomprising:an electrode formed on said supporting plate and connected tosaid control means; and an electric conductive wire, formed by wirebonding, for connecting said electrode to said film resistance pattern.18. An apparatus as set forth in claim 17 further comprising means forcovering said electric conductive wire.
 19. An apparatus as set forth inclaim 18, wherein said covering means has at least a curled edge toprotect said electric conductive wire.
 20. An apparatus as set forth inclaim 18, further comprising an adiabatic member inserted between saidcovering means and said substrate.
 21. An apparatus set forth in claim1, wherein said supporting plate supports at least one end of saidsubstrate by said adiabatic member.
 22. A measuring apparatus as inclaim 1 wherein said adiabatic member is partially in contact with bothsaid planar substrate and said supporting plate at a portion other thana portion of said planar substrate where said film resistance pattern isformed.
 23. A direct-heated flow measuring apparatus for measuring theflow rate with passage comprising:a planar substrate that is formed ofmonocrystalline silicon; a film resistance pattern formed partially atsaid substrate; a supporting plate, fixed to said passage, forsupporting said substrate, said supporting plate having good heatdissipation characteristics; at least one adiabatic member disposedbetween said substrate and said supporting plate; and electric powercontrol means, connected to said film resistance pattern, forcontrolling the heat generated by said film resistance pattern, saidadiabatic member being partially in contact with both said planarsubstrate and said supporting plate at a portion other than a portion ofsaid planar substrate where said film resistance pattern is formed,wherein a material of said adiabatic member is polyimid resin, andwherein said polyimid resin has a thickness of 50 to 60 μm.
 24. Adirect-heated flow measuring apparatus for measuring the flow ratewithin a passage comprising:a planar substrate that is formed ofmonocrystalline silicon; a film resistance pattern formed at a centralportion of said substrate; a supporting plate, fixed to said passage,for supporting at least one end of said substrate, said supporting platehaving good heat dissipation characteristics; means for throttling heattransfer between said substrate and said supporting plate; and electricpower control means, connected to said film resistance pattern, forcontrolling the heat generated by said film resistance pattern, whereinholes are provided in said supporting plate, said heat transferthrottling means comprising adiabatic chips fixed to said holes, saidsubstrate being fixed to said chips.
 25. A direct heated flow measuringapparatus for measuring the flow rate within a passage, comprising:aplanar substrate that is formed of monocrystalline silicon; a filmresistance pattern formed at the central portion of said substrate; asupporting plate fixed to said passage, for supporting at least one endof said substrate, said supporting plate being made of a metal materialhaving a relatively larger thermal conductivity than a thermalconductivity of an adiabatic member; said adiabatic member between saidsubstrate and said supporting plate, for throttling heat transferredbetween said substrate and said supporting plate; and electric powercontrol means, connected to said film resistance pattern, forcontrolling the heat generated by said film resistance pattern.